Thermally activated pressure booster for heat pumping and power generation

ABSTRACT

Thermally activated systems and related processes for raising the pressure of a gaseous working fluid are described. The systems and processes can be used for both winter heating and summer cooling with increased efficiency. They can also be used for other applications in need of an efficient thermally driven compressor, such as a power generation process.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is entitled to priority pursuant to 35 U.S.C. §119(e)to U.S. Provisional Patent Application No. 61/446,010, filed on Feb. 23,2011, and U.S. Provisional Patent Application No. 61/500,594, filed onJun. 23, 2011, which are hereby incorporated by reference herein in itsentirety.

STATEMENT OF GOVERNMENT LICENSE RIGHTS

This invention was made in part with government support under Grant No.1113100 awarded by the National Science Foundation Small BusinessInnovation Program. The U.S. government has certain rights in thisinvention.

BACKGROUND OF THE INVENTION

Heating and cooling in buildings use over 20% of the total energyconsumed in the United States. Vehicle air conditioners also consume asignificant portion of the transportation fuel. In addition, heating andcooling of process streams are also performed in the process industry,especially chemical industry and power generation industry. As the priceof energy goes up, it becomes more desirable to run heating and coolingsystems with solar thermal energy. Solar energy is plentiful during thehot summer days when the demand for air conditioning is greatest, andwhen the load on the electrical grid reaches its peak. Uses of solarwater heaters are taking off in many places, including southern Europeand China. Such systems typically have a large excess supply of heat onhot summer days. It would be desirable to use this excess heat for airconditioning to meet the high demand for cooling at such time.

However, the state-of-art lithium bromide (LiBr)-water absorptionsystem, a thermally activated heat pump (TAHP) for cooling applications,is not suitable for use in residential and light commercial heating andcooling applications, because it uses water as the refrigerant and asalt solution as the absorbent. Water has a low vapor pressure. Anyliving space heating and cooling systems using water as the workingfluid would have to operate at a rather deep vacuum, which makes thesystems bulky. Furthermore, LiBr is a salt, which is corrosive and canfreeze out if the operating conditions are not well controlled, whichmeans skilled personnel is often needed to service such TAHP systems. Inaddition, the LiBr-water absorption system is not suitable for winterheating when the ambient temperature is below water freezingtemperature, because water freezes at 0° C. Thus, LiBr-water absorptionheat pumps are often called “LiBr chillers,” i.e., they are used forchilling only. The LiBr-water absorption system typically needs heat ofgreater than 88° C. in order to avoid freeze out issues, rendering thesystem unsuitable for many solar water heaters.

A TARP can have a heating coefficient of performance (heating COP)significantly greater than 1, while a conventional gas or oil furnaceonly has a heating COP of less than 1. A good single-effect TARP intheory can have a heating COP of greater than 1.7, while a double-effectTARP in theory can have a heating COP of even greater. Therefore, byusing a TARP, the thermal energy needs for heating can be reduced morethan 40% with a single effect TAHP system and even more with a doubleeffect TARP system. Considering the huge amount of energy consumed byheating, a TARP for space heating is extremely attractive.

Unfortunately, such promising heat efficient technologies have not beencommercialized despite many years of research and development efforts.This is in part because of the lack of safe and efficient TAHPs. Thecurrently available TAHPs based on LiBr-water absorption or itsderivatives use pure water as the working fluid. They cannot be usedwhen the space heating is most needed, i.e., when the ambienttemperature is close to or below 0° C., because water freezes below 0°C.

In theory, ammonia can be used as a working fluid in both vaporcompression heat pumps and thermally activated heat pumps. However, oneof the problems with ammonia is that it is highly toxic, therefore isnot very desirable for residential and vehicular applications. Asecondary loop is needed in order to mitigate the toxicity issue, whichadds to the cost of the system. In addition, the heat of absorption ofammonia in water is much greater than the latent heat of ammoniavaporization. This requires large heat exchange duties for absorptioncooling and distillation column boiling in an ammonia-water absorptionheat pump system, which means a very large heat exchanger cost andsignificant thermal energy degradation in the heat exchangers. This inturn increases the cost and decreases the COP of such TAHPs. Even withthe so-called GAX system, which utilizes more effectively the heatreleased during the absorption process for distillation separation, thesingle effect heating COP of the ammonia-water system is only at about1.6, or a cooling COP of about 0.6, which is significantly lower thanthat of the LiBr absorption system, whose cooling COP is on the order of0.75. Ammonia also has other problems such as its corrosivity withcopper and aluminum, two of the best materials for making heatexchangers, and the needs for very clean, oil-free surface for heattransfer. These problems have greatly constrained the use of thermallyactivated heat pumps with ammonia as the working fluid for heating andfor air conditioning.

Murphy and Phillips proposed a thermally activated heat pump withCClF₂CHClF as the working fluid and ETFE (ethyl tetrahydro-furfurylether), a high boiling organic oxygenate with a molecular weight of 130,as the solvent. See Kevin P. Murphy and Benjamin A. Phillips,“DEVELOPMENT OF A RESIDENTIAL GAS-ABSORPTION HEAT PUMP”, submitted forpresentation at the 18th Intersociety Energy Conversion EngineeringConference Aug. 21-26, 1983, Orlando, Fla. Such a system does not havesome of the shortcomings suffered by the LiBr absorption chillers andammonia-water absorption heat pumps in terms of freezeout, corrosion,and toxicity. Based on their development work, Murphy and Phillipsprojected a cooling COP of 0.65 and a heating COP of 1.50. However, sucha process has not been commercialized, possibly in part due to thesuboptimal heat exchange scheme used by the developers and the higherviscosity and heat capacity of the solvent they chose. In addition, theworking fluid, CClF₂CHClF, has ozone depleting potential, thus is notdesirable.

There is an unmet need to improve the efficiency of heating and cooling.In particular, there is an unmet need of a TAHP for heating that canreplace the fuel burning heaters and electrical resistive heaters tothereby greatly reduce the energy consumption for heating, and a TAHPfor cooling that can use the heat provided by solar water heaters or thecooling water coming from a vehicle engine to thereby drastically reducethe energy need for cooling. The present invention meets such unmetneeds by providing a thermally activated system for increasing thepressure of a gaseous working fluid, i.e., a thermally activatedpressure booster, and its uses in applications such as a TAHP. Such asystem can also be used for power generation using low level heat.

BRIEF SUMMARY OF THE INVENTION

In one general aspect, the present invention relates to a thermallyactivated system for increasing the pressure of a gaseous working fluid.The system comprises a working fluid having a bubble point of less than20° C. when the working fluid is at 1 atm pressure, and a solventcomprising an organic oxygenate containing in its molecule at least oneoxygen atom (O) and at least one atom selected from the group consistingof nitrogen (N), sulfur (S), phosphorus (P), fluorine (F), and acombination thereof, and the dew point of the solvent is greater than130° C. when the solvent is at 1 atm.

According to an embodiment of the present invention, the thermallyactivated system comprises:

an absorber, in which a lower pressure, substantially gaseous stream ofa working fluid is absorbed into a lower pressure, liquid stream of anabsorbent to form a liquid solution;

a cooler that removes heat from the absorber;

a pressure boosting device that increases the pressure of the liquidsolution to obtain a higher pressure liquid solution; and

a generator that separates the higher pressure liquid solution into atleast a higher pressure, substantially vaporized stream of the workingfluid and a higher pressure, liquid stream of the absorbent;

wherein the working fluid has a bubble point of less than 20° C. whenthe working fluid is at 1 atm pressure; and the absorbent comprisescomponents of the working fluid and a solvent comprising an organicoxygenate containing in its molecule at least one oxygen atom (O) and atleast one atom selected from the group consisting of nitrogen (N),sulfur (S), phosphorus (P), fluorine (F), and a combination thereof, andthe dew point of the solvent is greater than 130° C. when the solvent isat 1 atm.

In another embodiment, the present invention relates to a thermallyactivated system for increasing the pressure of a gaseous working fluid,comprising:

an absorber, in which a lower pressure, substantially gaseous stream ofa working fluid is absorbed into a lower pressure, liquid stream of anabsorbent to form a liquid solution, wherein the working fluid isselected from the group consisting of R134a, dimethyl ether, R152a, CH₃I(R13I1), propane, isopropane, propylene, isobutane, n-butane, HFO1234yf,and a combination thereof, and the absorbent comprises components of theworking fluid and a solvent selected from the group consisting ofN-methyl-2-pyrrolidone (NMP), dimethyl sulfoxide (DMSO),dimethylformamide (DMF), dimethylacetamide (DMAc), and a combinationthereof;

a cooler that removes heat from the absorber;

a pressure boosting device that increases the pressure of at least aportion of the liquid solution to obtain a higher pressure liquidsolution;

a generator that separates the higher pressure liquid solution into atleast a higher pressure, substantially vaporized stream of the workingfluid and a higher pressure, liquid stream of the absorbent;

a condenser that substantially condenses at least a portion of thehigher pressure, substantially vaporized stream of the working fluid toobtain a substantially condensed stream of the working fluid;

a heat exchanger that cools at least a portion of the substantiallycondensed stream of the working fluid to obtain a sub-cooled stream ofthe working fluid, while heating another stream,

a pressure reducing device that reduces the pressure of at least aportion of the sub-cooled stream of the working fluid to obtain a lowerpressure stream of the working fluid;

an evaporator that at least partially vaporizes at least a portion ofthe lower pressure stream of the working fluid to obtain an at leastpartially vaporized stream of the working fluid, while removing heatfrom another heat source, wherein

the other heat source is heat from environment of an enclosed space or aprocess stream when the thermally activated system is used for heatingthe enclosed space or the process stream, or heat from an enclosed spaceor a process stream when the thermally activated system is used forcooling the enclosed space or the process stream, and

the other stream in the heat exchanger comprises at least a portion ofthe at least partially vaporized stream of the working fluid, heating ofwhich results in the lower pressure, substantially gaseous stream of theworking fluid, at least a portion of which is fed to the absorber;

a second heat exchanger that cools at least a portion of the higherpressure, liquid stream of the absorbent to obtain a sub-cooled, liquidstream of the absorbent; and

a second pressure reducing device that reduces the pressure of at leasta portion the sub-cooled, liquid stream of the absorbent to obtain thelower pressure, liquid stream of the absorbent, at least a portion ofwhich is fed to the absorber.

In another general aspect, the present invention relates to a thermallyactivated process for increasing the pressure of a gaseous workingfluid. The process comprises using a working fluid having a bubble pointof less than 20° C. when the working fluid is at 1 atm pressure, and asolvent comprising an organic oxygenate containing in its molecule atleast one oxygen atom (O) and at least one atom selected from the groupconsisting of nitrogen (N), sulfur (S), phosphorus (P), fluorine (F),and a combination thereof, and the dew point of the solvent is greaterthan 130° C. when the solvent is at 1 atm.

According to an embodiment of the present invention, the thermallyactivated process comprises:

absorbing a lower pressure, substantially gaseous stream of a workingfluid into a lower pressure, liquid stream of an absorbent in anabsorber to obtain a liquid solution;

removing heat from the absorber;

increasing the pressure of the liquid solution to obtain a higherpressure liquid solution; and

separating at least a portion of the higher pressure liquid solution ina generator to obtain at least a higher pressure, substantiallyvaporized stream of the working fluid and a higher pressure, liquidstream of the absorbent;

wherein the working fluid has a bubble point of less than 20° C. whenthe working fluid is at 1 atm pressure; and the absorbent comprisescomponents of the working fluid and a solvent comprising an organicoxygenate containing in its molecule at least one oxygen atom (O) and atleast one atom selected from the group consisting of nitrogen (N),sulfur (S), phosphorus (P), fluorine (F), and a combination thereof, andthe dew point of the solvent is greater than 130° C. when the solvent isat 1 atm.

According to another embodiment, the present invention relates to athermally activated process for increasing the pressure of a gaseousworking fluid, comprising:

absorbing a lower pressure, substantially gaseous stream of a workingfluid into a lower pressure, liquid stream of an absorbent in anabsorber to obtain a liquid solution, wherein the working fluid isselected from the group consisting of R134a, dimethyl ether, R152a, CH₃I(R13I1), propane, isopropane, propylene, isobutane, n-butane, HFO1234yf,and a combination thereof, and the absorbent comprises components of theworking fluid and a solvent selected from the group consisting ofN-methyl-2-pyrrolidone (NMP), dimethyl sulfoxide (DMSO),dimethylformamide (DMF), dimethylacetamide (DMAc), and a combinationthereof;

removing heat from the absorber;

increasing the pressure of at least a portion of the liquid solution bya pressure boosting device to obtain a higher pressure liquid solution;

separating at least a portion of the higher pressure liquid solution ina generator to obtain at least a higher pressure, substantiallyvaporized stream of the working fluid and a higher pressure, liquidstream of the absorbent;

substantially condensing at least a portion of the higher pressure,substantially vaporized stream of the working fluid in a condenser toobtain a substantially condensed stream of the working fluid;

cooling at least a portion of the substantially condensed stream of theworking fluid in a heat exchanger to obtain a sub-cooled stream of theworking fluid, while heating another stream;

reducing the pressure of at least a portion of the sub-cooled stream ofthe working fluid to obtain a lower pressure stream of the workingfluid;

vaporizing at least a portion of the lower pressure stream of theworking fluid in an evaporator to obtain an at least partially vaporizedstream of the working fluid, while removing heat from another heatsource, wherein

the other heat source in the vaporizing step is heat from environment ofan enclosed space or a process stream when the thermally activatedprocess is used for heating the enclosed space or the process stream, orheat from an enclosed space or a process stream when the thermallyactivated process is used for cooling the enclosed space or the processstream, and

the other stream in the heat exchanger comprises the at least partiallyvaporized stream of the working fluid from the evaporator, heating ofwhich results in the lower pressure, substantially gaseous stream of theworking fluid;

feeding at least a portion of the lower pressure, substantially gaseousstream of the working fluid to the absorber;

cooling at least a portion of the higher pressure, liquid stream of theabsorbent in a second heat exchanger to obtain a sub-cooled, liquidstream of the absorbent;

reducing the pressure of at least a portion of the sub-cooled, liquidstream of the absorbent to obtain the lower pressure, liquid stream ofthe absorbent; and

feeding at least a portion of the lower pressure, liquid stream of theabsorbent to the absorber.

Other aspects, features and advantages of the invention will be apparentfrom the following disclosure, including the detailed description of theinvention and its preferred embodiments and the appended claims.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The foregoing summary, as well as the following detailed description ofthe invention, will be better understood when read in conjunction withthe appended drawings. For the purpose of illustrating the invention,there are shown in the drawings embodiments which are presentlypreferred. It should be understood, however, that the invention is notlimited to the precise arrangements and instrumentalities shown.

In the drawings:

FIG. 1 shows an example of a single effect system according to anembodiment of the present invention;

FIG. 2 shows an example of a double effect system according to anembodiment of the present invention; and

FIG. 3 shows an example of a power generation system according to anembodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Various publications, articles and patents are cited or described in thebackground and throughout the specification; each of these references isherein incorporated by reference in its entirety. Discussion ofdocuments, acts, materials, devices, articles or the like which has beenincluded in the present specification is for the purpose of providingcontext for the present invention. Such discussion is not an admissionthat any or all of these matters form part of the prior art with respectto any inventions disclosed or claimed.

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood to one of ordinary skill inthe art to which this invention pertains. Otherwise, certain terms usedherein have the meanings as set in the specification. All patents,published patent applications and publications cited herein areincorporated by reference as if set forth fully herein. It must be notedthat as used herein and in the appended claims, the singular forms “a,”“an,” and “the” include plural reference unless the context clearlydictates otherwise.

DEFINITIONS

Absorbent: an absorbent is a liquid that absorbs a gas to form a liquidsolution in an absorber, typically accompanied by heat removal.

Absorber: an absorber is a piece of a process equipment in which a gasis dissolved in an absorbent, forming a liquid solution.

Bubble point: the temperature at which a liquid starts to vaporize. Fora pure component, the bubble point at 1 atm is its boiling point.

Coefficient of performance (COP) or cooling COP: the amount of heatlifted divided by the amount of energy used in the heat pumping process.

Heating COP: the amount of heat available for heating divided by theamount of energy used.

COP and heating COP are related by the following mathematical formula:Heating COP=1+COP

Cooling water: cooling water in the context of the present inventionrefers to a heat transfer medium. It comprises mainly of water, and cancontain other components such as ethylene glycol, alcohols, salt, etc.

Countercurrent heat exchanger: a heat exchanger in which the streambeing heated flows in the opposite direction from that being cooled,wherein the streaming being heated and the stream being cooled areseparated by a thermally conductive solid material, such as a sheetmaterial.

Desuperheating: cooling a vapor from a higher temperature to or close toits dew point.

Dew point of a fluid: the temperature at which a gas starts to condense.The dew point of a pure component at 1 atm is the same as the boilingpoint for the pure component.

Generator: a piece of process equipment in which a mixture is separatedinto two (or more) streams of different compositions. The fundamentalbehind separation in a generator in the context of this patent is thevolatility difference between the different components of the mixture. Aprocess unit operating on the same principle of the generator in thecontext of the present invention can also be called desorber ordistillation unit or evaporation unit or evaporator in some otherplaces. It differs from an electric generator which refers to anelectro-mechanical device that converts mechanical energy to electricalenergy.

Heat pump: a process system that can move heat from a lower temperatureto a higher temperature. A conventional air conditioner is considered anexample of a heat pump in the context of the present invention, as is aconventional refrigerator and a conventional heat pump that is used forspace heating when the outdoor temperature is below that of the space tobe heated.

Heat pumping: a process that moves heat from a lower temperature to ahigher temperature.

HFC: fluorohydrocarbon, a chemical compound comprising hydrogen (H),carbon (C), and fluorine (F) in its molecule.

Organic oxygenate: an organic compound comprising one or more oxygen (O)atoms in its molecule.

Polyol: an alcohol comprising multiple —OH groups in its molecule.Examples of polyol include, but are not limited to, ethylene glycol,diethylene glycol, and propylene glycol.

Solvent: a liquid that can dissolve a liquid and/or a gas component.

Subcooler: a heat exchanger that cools a liquid to a temperature lowerthan its dew point.

Superheating: heating a vapor from its dew point or close to its dewpoint to a higher temperature.

Thermally activated heat pump (TAHP): a heat pump that is principallydriven by the heat flow from a higher temperature heat source to a lowertemperature heat sink. For example, a conventional LiBr chiller is athermally activated heat pump.

Working fluid: a fluid in a heat pump, power generation system, or heatactivated pressure booster that changes its phase. In heating, airconditioning, and refrigeration applications, a working fluid is alsocalled refrigerant. The working fluid may contain up to 5% of a solventin certain embodiments in this patent.

Embodiments of the present invention relate to a non-ozone depleting oressentially non-ozone depleting working fluid and a solvent thatimproves the performance of a heat activated pressure booster, which canbe used in applications such as a TAHP or a power generator. The presentinvention relates to a lower cost, highly efficient thermally activatedheat pump and air conditioning system that works at a higher pressurethan the conventional LiBr chillers. They are capable of working atbelow sub water freezing temperatures, and can be thermally activated,especially with low level of heat, such as that from commercial solarwater heaters and the cooling water from vehicle engines. The heatactivated pressure booster according to embodiments of the presentinvention does not use corrosive materials, and has no potential issueof absorbent freeze out during operation.

In one general aspect, the present invention relates to a thermallyactivated system for increasing the pressure of a gaseous working fluid.The thermally activated system comprises:

an absorber, in which a lower pressure, substantially gaseous stream ofa working fluid is absorbed into a lower pressure, liquid stream of anabsorbent to form a liquid solution;

a cooler that removes heat from the absorber;

a pressure boosting device that increases the pressure of at least aportion of the liquid solution to obtain a higher pressure liquidsolution; and

a generator that separates at least a portion of the higher pressureliquid solution into at least a higher pressure, substantially vaporizedstream of the working fluid and a higher pressure, liquid stream of theabsorbent;

wherein the working fluid has a bubble point of less than 20° C. whenthe working fluid is at 1 atm pressure; and the absorbent comprisescomponents of the working fluid and a solvent comprising an organicoxygenate containing in its molecule at least one oxygen atom (O) and atleast one atom selected from the group consisting of nitrogen (N),sulfur (S), phosphorus (P), fluorine (F), and a combination thereof, andthe dew point of the solvent is greater than 130° C. when the solvent isat 1 atm.

According to another embodiment of the present invention, the thermallyactivated system further comprises:

a condenser that substantially condenses at least a portion of thehigher pressure, substantially vaporized stream of the working fluid toobtain a substantially condensed stream of the working fluid;

a pressure reducing device that reduces the pressure of at least aportion of the substantially condensed stream of the working fluid toobtain a lower pressure stream of the working fluid; and

an evaporator that at least partially vaporizes at least a portion ofthe lower pressure stream of the working fluid to obtain an at leastpartially vaporized stream of the working fluid, while removing heatfrom another heat source,

wherein the other heat source in the evaporator is heat from environmentof an enclosed space or a process stream when the thermally activatedsystem is used for heating the enclosed space or the process stream, orheat froman enclosed space or a process stream when the thermallyactivated system is used for cooling the enclosed space or the processstream.

It is readily understood by those of ordinary skill in the art that whena thermally activated system is used for heating an enclosed space orprocess stream, it can be used to heat the enclosed space or a processstream directly, or indirectly by heating a stream or medium that isused to heat the enclosed space or process stream. Thus, the other heatsource in the evaporator can be heat directly or indirectly from theenvironment.

Similarly, when a thermally activated system is used for cooling anenclosed space or process stream, it can be used to cool the enclosedspace or a process stream directly, or indirectly by cooling a stream ormedium that is used to cool the enclosed space or process stream. Thus,the other heat source in the evaporator can be heat directly orindirectly from the enclosed space or process stream.

Examples of the enclosed space or a process stream include, but are notlimited to, the space within a room or a building, or the space within avehicle, or a process stream in an industrial plant or installation. Theenvironment of an enclosed space or a process stream can be the spaceoutside of the enclosed space or process stream.

In another embodiment, the thermally activated system further comprisesa heat exchanger that cools at least a portion of the substantiallycondensed stream of the working fluid to obtain a sub-cooled stream ofthe working fluid, while heating another stream. At least a portion ofthe sub-cooled stream of the working fluid is then fed to the pressurereducing device to obtain the lower pressure stream of the workingfluid. The other stream heated in the heat exchanger comprises at leasta portion of the at least partially vaporized stream of the workingfluid from the evaporator, heating of which results in the lowerpressure, substantially gaseous stream of the working fluid, at least aportion of which is used in the absorber.

In another embodiment of the present invention, the thermally activatedsystem further comprises: a second pressure reducing device in fluidcommunication with the absorber, wherein the second pressure reducingdevice reduces the pressure of at least a portion of the higherpressure, liquid stream of the absorbent from the generator to obtainthe lower pressure, liquid stream of the absorbent, at least a portionof which is used in the absorber.

In yet another embodiment of the present invention, the thermallyactivated system further comprises a second heat exchanger in fluidcommunication with the pressure boosting device, an intermediatelocation of the generator, the bottom section of the generator, and thesecond pressure reducing device, wherein the second heat exchanger coolsat least a portion of the higher pressure, liquid stream of theabsorbent from the bottom section of the generator to obtain asub-cooled liquid stream of the absorbent, while heating and partiallyvaporizing at least a portion of the higher pressure, liquid solutionfrom the pressure boosting device to obtain a higher pressure, two-phasestream, which is subsequently fed to the intermediate location of thegenerator; and at least a portion of the sub-cooled liquid stream of theabsorbent is then fed to the second pressure reducing device to obtainthe lower pressure, liquid stream of the absorbent.

The intermediate location of the generator can be any location of thegenerator that is in between of the top and the bottom sections of thegenerator.

According to an embodiment of the present invention, the thermallyactivated system comprises more than one generator. For example, athermally activated system according to an embodiment of the presentinvention can comprise a higher pressure generator, and a mediumpressure generator having an operating pressure lower than that of thehigher pressure generator, wherein there is thermal communicationbetween the top section of the higher pressure generator and the mediumpressure generator.

In another embodiment, the present invention relates to a powergeneration system, which comprises the thermally activated systemaccording to an embodiment of the present invention and an expander,wherein at least a portion of the higher pressure, substantiallyvaporized stream of the working fluid from the generator is expanded inthe expander to generate mechanical energy, and at least a portion ofthe exhaust stream of the working fluid from the expander is absorbedinto the lower pressure, liquid stream of the absorbent in the absorber.

In another general aspect, the present invention relates to a thermallyactivated process for increasing the pressure of a gaseous workingfluid. The method comprises:

absorbing a lower pressure, substantially gaseous stream of a workingfluid into a lower pressure, liquid stream of an absorbent in anabsorber to obtain a liquid solution;

removing heat from the absorber;

increasing the pressure of at least a portion of the liquid solution toobtain a higher pressure liquid solution; and

separating at least a portion of the higher pressure liquid solution ina generator to obtain at least a higher pressure, substantiallyvaporized stream of the working fluid and a higher pressure, liquidstream of the absorbent;

wherein the working fluid has a bubble point of less than 20° C. whenthe working fluid is at 1 atm pressure; and the absorbent comprisescomponents of the working fluid and a solvent comprising an organicoxygenate containing in its molecule at least one oxygen atom (O) and atleast one atom selected from the group consisting of nitrogen (N),sulfur (S), phosphorus (P), fluorine (F), and a combination thereof, andthe dew point of the solvent is greater than 130° C. when the solvent isat 1 atm.

According to another embodiment of the present invention, the thermallyactivated process further comprises:

substantially condensing at least a portion of the higher pressure,substantially vaporized stream of the working fluid in a condenser toobtain a substantially condensed stream of the working fluid;

reducing the pressure of at least a portion of the substantiallycondensed stream of the working fluid to obtain a lower pressure streamof the working fluid; and

vaporizing at least a portion of the lower pressure stream of theworking fluid in an evaporator to obtain an at least partially vaporizedstream of the working fluid, while removing heat from another heatsource,

wherein the other heat source in the vaporizing step is heat fromenvironment of an enclosed space or a process stream when the thermallyactivated process is used for heating the enclosed space or processstream, or heat from the enclosed space or a process stream when thethermally activated process is used for cooling the enclosed space orprocess stream.

According to another embodiment of the present invention, the thermallyactivated process further comprises cooling at least a portion of thesubstantially condensed stream of the working fluid in a heat exchangerto obtain a sub-cooled stream of the working fluid, while heatinganother stream, wherein at least a portion of the sub-cooled stream ofthe working fluid is then fed to the pressure reducing device, and theother stream comprises at least a portion of the at least partiallyvaporized stream of the working fluid from the evaporator, heating of atleast a portion of which results in the lower pressure, substantiallygaseous stream of the working fluid, at least a portion of which is usedin the absorber.

In another embodiment of the present invention, the thermally activatedprocess further comprises:

reducing the pressure of at least a portion of the higher pressure,liquid stream of the absorbent from the generator to obtain the lowerpressure, liquid stream of the absorbent; and

feeding at least a portion of the lower pressure, liquid stream of theabsorbent to the absorber.

In yet another embodiment of the present invention, the thermallyactivated process further comprises:

cooling at least a portion of the higher pressure, liquid stream of theabsorbent obtained from the bottom section of the generator in a secondheat exchanger to obtain a sub-cooled, liquid stream of the absorbent,while heating and partially vaporizing at least a portion of the higherpressure, liquid solution from the pressure boosting device to obtain ahigher pressure, two-phase stream;

feeding at least a portion of the higher pressure, two-phase stream toan intermediate location of the generator; and

feeding at least a portion of the sub-cooled liquid stream of theabsorbent to the second pressure reducing device to obtain the lowerpressure, liquid stream of the absorbent.

According to an embodiment of the present invention, the thermallyactivated process utilizes more than one generators in the separatingstep. For example, a thermally activated process according to anembodiment of the present invention can comprise using a higher pressuregenerator, and a medium pressure generator having an operating pressurelower than that of the higher pressure generator in the separating step,wherein there is thermal communication between the top section of thehigher pressure generator and the medium pressure generator.

In another embodiment, the thermally activated process is used forgenerate a power. The process further comprises:

expanding at least a portion of a higher pressure, substantiallyvaporized stream of the working fluid in an expander to generatemechanical energy; and

absorbing at least a portion of the exhaust stream of the working fluidfrom the expander into the lower pressure, liquid stream of theabsorbent in the absorber.

In an embodiment of the present invention, the working fluid comprises acomponent selected from the group consisting of R134a(1,1,1,2-tetrafluoroethane), dimethyl ether, R152a (F₂HC-CH₃), CH₃I(R13I1), propylene, propane, cyclopropane, isobutane, n-butane,HFO1234yf, and a combination thereof.

In another embodiment of the present invention, the solvent is selectedfrom the group consisting of an organic oxygenate containing in itsmolecule at least one atom selected from the group consisting ofnitrogen (N), phosphorus (P), fluorine (F), and sulfur (S), and acombination thereof, has a dew point of greater than 130° C. when thesolvent is at 1 atm, and has a viscosity of less than 2.5 cP at 20° C.

In an embodiment of the present invention, the solvent is selected fromthe group consisting of N-methyl-2-pyrrolidone (NMP), dimethyl sulfoxide(DMSO), dimethylformamide (DMF), dimethylacetamide (DMAc), and acombination thereof.

The absorbent contains both the working fluid and the solvent. Theabsorbent is also referred to as the working fluid lean solution in thepresent application.

The absorption of a working fluid into an absorbent in the absorber orthe absorbing step forms a liquid solution rich in the working fluid.The liquid solution is also referred to as the weak solution in thepresent application.

In an embodiment of the present invention, the higher pressure, liquidsolution from the pressure boosting device is split into at least amajor stream and a minor stream. The minor stream constitutes 1-20%(mol) of the total flow of the higher pressure, liquid solution and isfed to the top of the generator. The major stream is heated andpartially vaporized in a heat exchanger to obtain a two-phase stream,i.e., liquid and vapor, which is fed to an intermediate location of thegenerator.

In another embodiment of the present invention, a subcooler is used tocool at least a portion of the substantially condensed working fluidfrom the condenser, and heat and further vaporize at least a portion ofthe at least partially vaporized stream of the working fluid from theevaporator, which can contain 0.1-5% (mol) liquid.

FIG. 1 shows an example of a single effect absorption heat pump processaccording to an embodiment of the present invention. In this process, alower pressure, substantially gaseous stream of a working fluid (306)and a lower pressure, liquid stream of an absorbent (314) are fed intoan absorber (31) to obtain a liquid solution (308). The resultantworking fluid-rich solution or weak solution (308) is fed to a pump (32)to obtain a higher pressure weak solution (309), which is subsequentlysplit into a major stream (310) and a minor stream (312). The major weaksolution stream (310), typically 80-99% (mol) of the weak solution, isheated and partially vaporized in a substantially countercurrent heatexchanger (33), and the resultant higher pressure two-phase stream in(311) is fed to the lower feeding port of the generator (34), located inan intermediately position of the generator (34), while the minor higherpressure weak solution (312), typically 1-20% (mol) of the total of theweak solution, is fed to a higher feeding port of the generator (34)without being heated. The generator (34), which is a distillationcolumn, produces a higher pressure vapor working fluid (301), and abottoms liquid (313), i.e., the absorbent that is lean in the componentsof the working fluid.

The overhead higher pressure vapor working fluid (301) is condensed incondenser (35), releasing heat. The resultant substantially condensedworking liquid is split into two streams: the reflux (315), which flowsback to the top of the generator (34); and the rest (303) to besubcooled in a substantially countercurrent heat exchanger or Subcooler(30). The reflux stream (315) for this system is a very small fractionof the total working fluid coming out of the condenser, typicallysmaller than 10% (mol) of the total working fluid flow in the condenser.Heat, Q_(g), is supplied to the base or the bottom section of thegenerator (34) to provide the reboiling heat of the distillation column.This heat transfer can be carried out in a heat exchanger inside oroutside the generator.

The substantially condensed working fluid (303) is cooled by the lowerpressure, mostly vaporized stream (305 a) of the working fluid from theevaporator (13) in a subcooler (30) that is a substantiallycounter-current heat exchanger. The resultant sub-cooled or coolerworking fluid (304) is reduced in pressure in throttle valve (12). Thisresults in a two phase stream at a lower temperature (305). This lowertemperature, two phase stream (305) is heated and mostly vaporized inthe evaporator (13). External heat (110), which can be from theenvironment when the system is used for heating, or room air or aprocess stream to be cooled when the system is used for cooling, is usedto vaporize most of the two phase stream (305). Cooling of the externalheat stream (110) results in a lower temperature stream (112). Thetemperature of the lower temperature stream (112) is lower than that ofstream 303. The mostly vaporized working fluid (305 a) is firstsubstantially completely vaporized and further heated in the subcooler(30). The resultant lower pressure, substantially gaseous working liquid(306) is then used for absorption by the absorbent (314) in the absorber31, releasing heat (Qb) at a temperature higher than that of stream 112.This heat removal can be carried out in one or more heat exchanger(s)inside the absorber.

The higher pressure absorbent (313) is cooled in the substantiallycounter-current heat exchanger (33), and let down in pressure in athrottle valve (36) to produce the lower pressure absorbent stream(314), which is used for absorption in the absorber (31).

The unique heat exchange schemes in this process allows for asignificantly higher efficiency. Due to the very low pressure in LiBrchillers, the LiBr chillers are not suitable to perform at least some ofthe technical features of heat exchange schemes according to embodimentsof the present invention.

To simplify the system, the reflux stream (315) to the top of thegenerator (34) can be eliminated, and the minor feed stream (312) is fedto where reflux is typically fed in the generator (34). In that case,the working fluid (301) will contain some small fraction of the solvent.To mitigate this situation, the working fluid (305 a) coming out of theevaporator (13) is allowed to contains some liquid, typically in 0.1-5%(mol) range. We discovered that when a substantially countercurrentsubcooler (30) is used to cool the substantially condensed working fluid(303) from the condenser with the further vaporization and heating ofthe mostly vapor working fluid (305 a) coming from the evaporator,essentially all of the remaining liquid in the working fluid (305 a) canbe vaporized in the subcooler (30). It is surprisingly discovered fromour simulation study that such a simplification not only does not causeefficiency penalties, but on the contrary, the cooling COP value isincreased by about 1%. We therefore consider this a preferredembodiment.

Embodiments of the present invention also include two or more effectheat pumps and their uses thereof.

FIG. 2 shows an example of a double effect system. The differencebetween this process and that in FIG. 1 described as follows. The higherpressure liquid solution coming out of the pump (55) is split into twostreams. The stream (409) is let down in pressure in throttle valve (67)to a medium pressure that is higher than that of the solution (408)upstream of the pump (55). The resultant medium pressure solution isfurther split into the major portion (410) and the minor portion (412).The major portion (410) of the medium pressure solution is heated andpartially vaporized in a substantially countercurrent medium pressureheat exchanger (56), and the resultant medium pressure two phase stream(411) is fed to the lower feeding port of a medium pressure generator(57). The minor medium pressure stream (412) is fed directly to thehigher feeding port of the medium pressure generator (57). The mediumpressure generator (57) generates an overhead, medium pressure,substantially vaporized stream (431) of the working fluid. It alsogenerates a medium pressure absorbent (413), which is lean in theworking fluid components, from the bottom. The medium pressure absorbent(413) is then cooled in the medium pressure bottom subcooler (56), whichis a substantially countercurrent heat exchanger. The resultantsubcooled medium pressure lean liquid is further let down in pressure inthrottle valve (59).

Another portion of the high pressure solution (420) from the pump (55)is first heated in a substantially countercurrent high pressure heatexchanger (68). A side stream (422) is taken out of the heat exchanger(68) and fed to a higher feeding port in a higher pressure generator(69). The remaining portion of the heated higher pressure liquidsolution is further heated and partially vaporized in the substantiallycountercurrent high pressure heat exchanger (68), and the resultant twophase high pressure stream (421), is fed to the lower feeding port ofthe higher pressure generator (69). The higher pressure generator (69)is heated by heat Qg at the base or the lower section. The higherpressure generator (69) produces a higher pressure vapor stream (423)that is substantially composed of the working fluid from the top, and aworking fluid-lean stream or absorbent (425) from the bottom.

The higher pressure overhead vapor stream (423) is condensed in thereboiler/condenser (60), which resides in the bottom section of themedium pressure column (57). The resultant higher pressure condensate,which is essentially pure working fluid, is split into two streams: thereflux (433), which is sent back to the top of the higher pressuregenerator (69), and the rest (424) is further subcooled in the subcooler(61). This subcooler (61) can be a part of the medium pressure generator(57). That is to say, the higher pressure working fluid solution can besubcooled in the medium pressure generator (57) by the substantiallycountercurrent heat exchanger 61. The subcooled, higher pressure liquidworking fluid is then let down in pressure in throttle valve 62, forminga two phase stream, and join the overhead working fluid vapor (431) fromthe medium pressure generator (57).

The combined medium pressure working fluid (401), formed from thevaporized working fluid from the top of the medium pressure column andthe two phase mixture from valve (62) is fed to the condenser (58),releasing heat. The resultant condensed liquid working fluid, is splitinto two streams: the reflux (432), which is fed back to the top of themedium pressure generator (57), and the liquid working fluid (403), tobe subcooled in a medium pressure top subcooler (50), which is asubstantially countercurrent heat exchanger.

The absorbent stream (425) from the high pressure generator (69) issubcooled in a higher pressure, substantially countercurrent heatexchanger (68). The resultant subcooled absorbent stream (426), is firstlet down in pressure higher pressure in throttle valve (63). The thusresultant lower pressure absorbent stream (427) is then combined withthe absorbent stream from throttle valve (59) and form a low pressureabsorbent stream (428), which is then fed to the absorber (54) forreuse.

The other parts of this process are similar to those of FIG. 1.

Similarly, one or both of the refluxes (433) and (432) to the high andmedium pressure generators, respectively, can also be eliminated, andthe minor feed streams (422) and (412) can be fed to the tops of thehigh and medium pressure generators, respectively. In such a case, theworking fluid (431) and (423), coming out of the tops of the generatorswill contain some solvent, typically in 10 ppm-5% range. In such a case,the working fluid stream (305 a) leaving the evaporator (53) shouldpreferably contains 0.1-5% (mol) liquid, and is then substantiallycompletely vaporized in the subcooler (50).

In view of the present disclosure, those skilled in the art wouldreadily appreciate that systems and processes according to embodimentsof the present invention can be used for heating or cooling an enclosedspace or process stream, such as the interior of a building or a vehicleor a process stream in an industrial process. When the systems are usedfor cooling, the evaporator removes heat from the enclosed space or aprocess stream while heat from the condenser and the absorber isexpelled to the environment. When the systems are used for heating, theevaporator absorbs heat from the environment while the condenser and theabsorber provide heat to the enclosed space or process stream. A unitarysystem can be built such that the same system can be used for bothwinter heating and summer cooling, e.g., by switching the roles of thecondenser and the evaporator as season changes.

In order to reduce the global warming potential (GWP) of the workingfluid and still keep the working fluid inflammable, in a preferredembodiment, the work fluid comprises a blend of one or more organiccomponents, such as R134a, CF₃I, DMF, or HFO1234yf. DME is selected inthe example due to its excellent thermodynamic properties, low cost,non-toxicity, low GWP nature, and a slightly higher boiling point thanthat of R134a. R134a is used to make the working fluid inflammable. Dueto the very close boiling points of the components, such mixtures behavevery much like azeotropes. CF₃I has a GWP value of 1. Therefore, amixture of CF₃I and DME has a very low GWP value. On the other hand, themixture of CF₃I and DME is considered to have some ozone depletingpotential (ODP) although its ODP value is very small (less than 0.008,likely less than 0.0001 of R11). HFO1234yf has a GWP of about 4, vs. the1430 value for R134a, but is slightly flammable.

Many hydrocarbons and organic oxygenates have the desired properties ofhaving a boiling point of greater than 130° C. (or dew point of greaterthan 130° C. at 1 atm for mixed solvents), that are relativelyinexpensive and miscible with the above-mentioned working fluids, thuscan be used as the solvent. Examples include the base oil of lube oils,polyols such as ethylene glycol, triethylene glycol, propylene glycol,dipropylene glycol, glymes such as tetraglyme, or the products of thecondensation reactions between glycols and ketones or aldehydes. Thebase oils of lube oils, tetraglyme (or a combination of glymes such asthat used in the Solexol process), ethylene glycol, and triethyleneglycol are among the common commodity chemicals with relatively low unitprice and low toxicity and therefore are among our initial candidatesfor study.

Simulations of the system with several solvents, including cetane,ethylene glycol, diethylene glycol, triethylene glycol, and tetraglymewere run. It was found that the systems with low molecular weightorganic oxygenates containing atoms selected from N, P, F, and S, andwhose boiling points are greater than 130° C. such asN-methyl-2-pyrrolidone (NMP), dimethyl sulfoxide (DMSO),dimethylformamide (DMF), and dimethylacetamide (DMAc), as the solventhave higher COP values and much lower heat exchanger UA values due totheir smaller molecular mass (e.g., 99 g/mol for NMP, 78 for DMSO, 73for DMF, and 87 for DMAc vs. 280 g/mol for tetraglyme) and lowerspecific heat (e.g., 0.40 for NMP, vs. 0.49 for tetraglyme). They shouldalso have much greater heat transfer coefficients due to the relativelylow viscosity (1.65 cP for NMP, 2.0 for DMSO, 0.92 for DMF, and 2.0 forDMAc vs. 5.8 cP for tetraglyme at 20° C.).

For example, the other physical, health, and flammability properties ofNMP are shown below:

BOILING POINT: 396° F. (202° C.) FREEZING POINT: −11° F. (−24° C.) FLASHPOINT: 199° F. (93° C.) AUTOIGNITION: 518° F. (270° C.) EXPLOSIONLIMITS: LEL: 0.99%, UEL: 3.9% TOXICITY DATA: 3,914 mg/kg oral-rat LD50

Those for DMSO are as follows:

BOILING POINT: 372° F. (189° C.) FREEZING POINT: 66° F. (19° C.) FLASHPOINT: 192° F. (89° C.) AUTOIGNITION: 419° F. (215° C.) EXPLOSIONLIMITS: LEL: 2.6%, UEL: 42% TOXICITY DATA: Acute oral toxicity (LD50):7920 mg/kg [Mouse] Acute dermal toxicity (LD50): 40000 mg/kg [Rat]

Those for DMF are as follows:

BOILING POINT: 307° F. (153° C.) FREEZING POINT: −78° F. (−61° C.) FLASHPOINT: 136.4° F. (58° C.) AUTOIGNITION: 833° F. (445° C.) EXPLOSIONLIMITS: LEL: 2.2%, uel: 15.2% TOXICITY DATA: ORL-RAT LD50 2800 mg kg⁻¹IPR-RAT LD50 1400 mg kg⁻¹ IVN-RAT LD50 2000 mg kg⁻¹ IPR-RBT LD50 1000 mgkg⁻¹

Those for DMAc are as follows:

BOILING POINT: 325.4° F. (165° C.) FREEZING POINT: −1.5° F. (−18.6° C.)FLASH POINT: 150.8° F. (66° C.) AUTOIGNITION: 914° F. (490° C.)EXPLOSION LIMITS: LEL: 1.8%, UEL: 11.5% TOXICITY DATA: Acute oraltoxicity (LD50): 7920 mg/kg [Mouse]. Acute dermal toxicity (LD50): 40000mg/kg [Rat].

In a preferred embodiment, NMP was chosen as the solvent in thedescription below because of its overall superior performance. However,other components in the family can also have more desirable values oncertain properties. Thus, components, including, but not limited to,DMSO, DMF, DMAc, NMP, or a combination of one or more of thesecomponents, can be the preferred solvent under certain specificconditions.

While the flow sheets in FIGS. 1 and 2 show that the bottoms liquids ofthe generators are cooled by exchanging heat with the feed streams tothe generators in substantially counter-current heat exchangers outsidethe generators, these streams can also be cooled inside the columnagainst the falling liquids in the generators. In the absorber, the workfluid rich liquid from the bottom of the absorber after it is reduced inpressure can be used to absorb some of the heat released from theabsorption by exchanging heat with the streams inside the absorber.

A heat pump system according to an embodiment of the present inventionis suitable for living space cooling or heating in residential andvehicular applications as well as in commercial applications. Use ofsuch a system for heating can greatly decrease the fuel consumption,while for air conditioning applications it can use solar water heater orthe cooling water coming out of the vehicle engines, thereby drasticallyreducing the electricity demand for air conditioning during the hotsummer days when the demand for electricity reaches peaks, or thatgenerated by burning liquid fuel, which is expensive and is becomingeven more expensive.

Note that a thermally activated system according to embodiments of thepresent invention is based on the principle that such an absorptionsystem can act as a thermally driven compressor. There can be other usesof such a thermal compressor. For example, in principle, an expander canbe used for power generation in the placed of the condenser-vaporizer.

FIG. 3 shows such a process. In this process, the absorption—separationparts are the same as those in the process in FIG. 1. The difference isthat in this process a vapor stream (501) is directly taken out of thetop of the generator (34), and expanded in an expander (70). The workobtained from expander (70) can be used to generate electricity by anelectric generator (72), which is mechanically connected to the expander(70). The resultant low pressure vapor (502), is then sent to theabsorber (31) for further use. The vapor stream (501) coming out of thegenerator can be further heated before it is fed to the expander (70).This is not shown in FIG. 3.

It is possible to have the components of a heat pump: the condenser,subcooler, pressure reducing valve, and evaporator, and an expander inparallel with switching valves so that the system can be used as athermally activated heat pump when heating or cooling is needed, and canbe used as a power generation system when either heating nor cooling isneeded, or even used both as a heat pump and a power generation system.

The following examples are provided to enable one skilled in the art topractice the invention and are merely illustrative of the invention. Theexamples should not be read as limiting the scope of the invention asdefined in the claims.

EXAMPLE

The system in FIG. 1 with NMP as the solvent and R134a-DME mix as theworking fluid was simulated for heating and cooling applications. Theresults are listed in Table 1.

In table 1, subscript b stands for absorber cooler, c for generatorcondenser, e for evaporator, and g for the generator heater. Note thegenerator heat duty is distributed among the feeding stage and the 3stages in the stripping section (including the bottom stage) in thesimulation, so most of the heat absorption takes place at temperaturesbelow T_(g). That can be important if the heat is provided in the formof sensible heat. The CCOP and HCOP values are the thermal COP values:CCOP=evaporator duty/reboiler duty, HCOP=(condenser duty+absorber coolerduty)/reboiler duty.

TABLE 1 The temperatures of the absorber cooler, condenser, evaporator,and generator reboiler, pressures, working fluid composition, as well asthe CCOP and HCOP values Tb Tc Te Tg pe Pg DME/R134a HCOP Case (mode) (°C.) (° C.) (° C.) (° C.) atm Atm (mass) (CCOP) 1. Heating 27.3 27.3 4.687 3.3 6.8 23.2/76.8 1.90 2. Heating 27.4 27.2 −8.3 226.2 2.0 6.823.9/76.1 1.81 3. Cooling 36.4 36.7 14.3 75.9 4.4 8.7 38.0/62.0 (0.83)4. Cooling 36.4 36.7 14.3 71 4.4 8.7 56.6/43.4 (0.78)

TABLE 2 Composition of the weak and strong absorbent in the four casesCase 1 2 3 4 Weak solution composition (mol frac) DME .09690 .1690 .2722.2722 R134a .09690 .1690 .1270 .1270 NMP .8062 .6619 .6007 .6007Absorbent composition (mol frac) DME .06975 .1125 .2307 .2481 R134a.05204 .07036 .08626 .1018 NMP .8782 .8172 .6831 .6501

The other conditions used in the simulation were as follows: thegenerator had 6 theoretical stages (2 stages in the rectifying section,and 4 in the stripping section including the feed stage), and theabsorber had only one stage (i.e., it is a mixer). Our later studyshowed that the number of stages in the generator could be reduced to 3to 4 stages without significantly impacting the performance of thesystem when the working fluid coming out of the evaporator was allowedto contain a few percent of liquid, which was then substantiallyvaporized in the substantially countercurrent subcooler. The pump work(60% pump efficiency and 95% motor efficiency were assumed) values wererespectively 0.8%, 2.1%, 1.4% %, and 2.3% of the generator reboilerduties of the respective cases.

The compositions of the strong absorbent and weak absorbent for the fourcases are shown in Table 2.

As can be seen, a HCOP of 1.90 can be achieved for heating when theevaporator temperature is 40.4° F. (4.7° C.), the condenser and absorbercooler temperatures are about 81° F. (27° C.), and the generatorreboiler temperature is 188° F. (87° C.). When the ambient temperatureis lower, such as when the evaporator temperature is 17° F. (−8° C.),the HCOP is reduced while the temperature of the generator reboiler isincreased to 226.5° F. (108° C.). When the unit is used for cooling, ifthe evaporator temperature is 57.7° F. (14.3° C.), and the condenser andabsorber cooler temperature are at about 98° F. (37° C.), the CCOP canbe 0.83 if the generator reboiler is at 170° F. (76.7° C.), or 0.78 ifthe generator reboiler is at 160° F. (71° C.).

The latter two cases showed that such a chiller can be driven by the hotwater from the low cost flat panel solar collectors and the system canstill give a CCOP of significantly greater than the typical 0.6-0.75value of the LiBr absorption chillers and aqua-ammonia absorption heatpumps driven by higher temperature heat sources.

It will be appreciated by those skilled in the art that changes could bemade to the embodiments described above without departing from the broadinventive concept thereof. It is understood, therefore, that thisinvention is not limited to the particular embodiments disclosed, but itis intended to cover modifications within the spirit and scope of thepresent invention as defined by the appended claims.

1. A thermally activated system for increasing the pressure of a gaseousworking fluid, comprising a working fluid having a bubble point of lessthan 20° C. when the working fluid is at 1 atm pressure, and a solventcomprising an organic oxygenate containing in its molecule at least oneoxygen atom (O) and at least one atom selected from the group consistingof nitrogen (N), sulfur (S), phosphorus (P), fluorine (F), and acombination thereof, and the dew point of the solvent is greater than130° C. when the solvent is at 1 atm.
 2. The thermally activated systemof claim 1, comprising: an absorber, in which a lower pressure,substantially gaseous stream of the working fluid is absorbed into alower pressure, liquid stream of an absorbent to form a liquid solution,wherein the absorbent comprises components of the working fluid and thesolvent; a cooler that removes heat from the absorber; a pressureboosting device that increases the pressure of at least a portion of theliquid solution to obtain a higher pressure liquid solution; and agenerator that separates at least a portion of the higher pressureliquid solution into at least a higher pressure, substantially vaporizedstream of the working fluid and a higher pressure, liquid stream of theabsorbent.
 3. The thermally activated system of claim 2, furthercomprising: a condenser that substantially condenses at least a portionof the higher pressure, substantially vaporized stream of the workingfluid to obtain a substantially condensed stream of the working fluid; apressure reducing device that reduces the pressure of at least a portionof the substantially condensed stream of the working fluid to obtain alower pressure stream of the working fluid; and an evaporator that atleast partially vaporizes at least a portion of the lower pressurestream of the working fluid to obtain an at least partially vaporizedstream of the working fluid, while removing heat from another heatsource, wherein the other heat source in the evaporator is heat fromenvironment of an enclosed space or a process stream when the thermallyactivated system is used for heating the enclosed space or the processstream, or heat from an enclosed space or a process stream when thethermally activated system is used for cooling the enclosed space or theprocess stream.
 4. The thermally activated system of claim 3, furthercomprising a heat exchanger that cools at least a portion of thesubstantially condensed stream of the working fluid from the condenserto obtain a sub-cooled stream of the working fluid, while heatinganother stream, wherein at least a portion of the sub-cooled stream ofthe working fluid is subsequently fed to the pressure reducing device toobtain the lower pressure stream of the working fluid, and the otherstream in the heat exchanger comprises at least a portion of the atleast partially vaporized stream of the working fluid from theevaporator, heating of which results in the lower pressure,substantially gaseous stream of the working fluid, at least a portion ofwhich is fed to the absorber.
 5. The thermally activated system of claim3, wherein the working fluid is selected from the group consisting ofR134a, dimethyl ether, R152a, CH₃I (R13I1), propane, isopropane,propylene, isobutane, n-butane, HFO1234yf, and a combination thereof,and the solvent has a viscosity of less than 2.5 cP at 20° C.
 6. Thethermally activated system of claim 3, wherein the solvent is selectedfrom N-methyl-2-pyrrolidone (NMP), dimethyl sulfoxide (DMSO),dimethylformamide (DMF), dimethylacetamide (DMAc), and a combinationthereof.
 7. The thermally activated system of claim 1, comprising: anabsorber, in which a lower pressure, substantially gaseous stream of aworking fluid is absorbed into a lower pressure, liquid stream of anabsorbent to form a liquid solution, wherein the working fluid isselected from the group consisting of R134a, dimethyl ether, R152a, CH₃I(R13I1), propane, isopropane, propylene, isobutane, n-butane, HFO1234yf,and a combination thereof, and the absorbent comprises components of theworking fluid and a solvent selected from the group consisting ofN-methyl-2-pyrrolidone (NMP), dimethyl sulfoxide (DMSO),dimethylformamide (DMF), dimethylacetamide (DMAc), and a combinationthereof; a cooler that removes heat from the absorber; a pressureboosting device that increases the pressure of at least a portion of theliquid solution to obtain a higher pressure liquid solution; a generatorthat separates the higher pressure liquid solution into at least ahigher pressure, substantially vaporized stream of the working fluid anda higher pressure, liquid stream of the absorbent; a condenser thatsubstantially condenses at least a portion of the higher pressure,substantially vaporized stream of the working fluid to obtain asubstantially condensed stream of the working fluid; a heat exchangerthat cools at least a portion of the substantially condensed stream ofthe working fluid to obtain a sub-cooled stream of the working fluid,while heating another stream, a pressure reducing device that reducesthe pressure of at least a portion of the sub-cooled stream of theworking fluid to obtain a lower pressure stream of the working fluid; anevaporator that at least partially vaporizes at least a portion of thelower pressure stream of the working fluid to obtain an at leastpartially vaporized stream of the working fluid, while removing heatfrom another heat source, wherein the other heat source is heat fromenvironment of an enclosed space or a process stream when the thermallyactivated system is used for heating the enclosed space or the processstream, or heat from an enclosed space or a process stream when thethermally activated system is used for cooling the enclosed space or theprocess stream, and the other stream in the heat exchanger comprises atleast a portion of the at least partially vaporized stream of theworking fluid, heating of which results in the lower pressure,substantially gaseous stream of the working fluid, at least a portion ofwhich is fed to the absorber; a second heat exchanger that cools atleast a portion of the higher pressure, liquid stream of the absorbentto obtain a sub-cooled, liquid stream of the absorbent; and a secondpressure reducing device that reduces the pressure of at least a portionthe sub-cooled, liquid stream of the absorbent to obtain the lowerpressure, liquid stream of the absorbent, at least a portion of which isfed to the absorber.
 8. The thermally activated system of claim 7,wherein the second heat exchanger cools at least a portion of the higherpressure, liquid stream of the absorbent from the bottom section of thegenerator to obtain the sub-cooled liquid stream of the absorbent, whileheating and partially vaporizing at least a portion of the higherpressure, liquid solution from the pressure boosting device to obtain ahigher pressure, two-phase stream, which is subsequently fed to anintermediate location of the generator.
 9. The thermally activatedsystem of claim 1, comprising more than one generators.
 10. A powergeneration system, comprising the thermally activated system of claim 2and an expander, wherein at least a portion of the higher pressure,substantially vaporized stream of the working fluid from the generatoris expanded in the expander to generate mechanical energy, and at leasta portion of the exhaust stream of the working fluid from the expanderis absorbed into the lower pressure, liquid stream of the absorbent inthe absorber.
 11. A thermally activated process for increasing thepressure of a gaseous working fluid, comprising using a working fluidhaving a bubble point of less than 20° C. when the working fluid is at 1atm pressure, and a solvent comprising an organic oxygenate containingin its molecule at least one oxygen atom (O) and at least one atomselected from the group consisting of nitrogen (N), sulfur (S),phosphorus (P), fluorine (F), and a combination thereof, and the dewpoint of the solvent is greater than 130° C. when the solvent is at 1atm.
 12. The thermally activated process of claim 11, comprising:absorbing a lower pressure, substantially gaseous stream of the workingfluid into a lower pressure, liquid stream of an absorbent in anabsorber to obtain a liquid solution, wherein the absorbent comprisescomponents of the working fluid and the solvent; removing heat from theabsorber; increasing the pressure of at least a portion of the liquidsolution to obtain a higher pressure liquid solution; and separating atleast a portion of the higher pressure liquid solution in a generator toobtain at least a higher pressure, substantially vaporized stream of theworking fluid and a higher pressure, liquid stream of the absorbent. 13.The thermally activated process of claim 12, further comprising:substantially condensing at least a portion of the higher pressure,substantially vaporized stream of the working fluid in a condenser toobtain a substantially condensed stream of the working fluid; reducingthe pressure of at least a portion of the substantially condensed streamof the working fluid to obtain a lower pressure stream of the workingfluid; and vaporizing at least a portion of the lower pressure stream ofthe working fluid in an evaporator to obtain an at least partiallyvaporized stream of the working fluid, while removing heat from anotherheat source, wherein the other heat source in the vaporizing step isheat from environment of an enclosed space or a process stream when thethermally activated process is used for heating the enclosed space orthe process stream, or heat from the an enclosed space or a processstream when the thermally activated process is used for cooling theenclosed space or the process stream.
 14. The thermally activatedprocess of claim 13, further comprising: cooling at least a portion ofthe substantially condensed stream of the working fluid in a heatexchanger to obtain a sub-cooled stream of the working fluid, whileheating another stream, wherein the other stream in the heat exchangercomprises at least a portion of the at least partially vaporized streamof the working fluid from the evaporator, and heating of which resultsin the lower pressure, substantially gaseous stream of the workingfluid; feeding at least a portion of the lower pressure, substantiallygaseous stream of the working fluid to the absorber; and reducing thepressure of at least a portion of the sub-cooled stream of the workingfluid to obtain the lower pressure stream of the working fluid.
 15. Athermally activated process for increasing the pressure of a gaseousworking fluid, comprising: absorbing a lower pressure, substantiallygaseous stream of a working fluid into a lower pressure, liquid streamof an absorbent in an absorber to obtain a liquid solution, wherein theworking fluid is selected from the group consisting of R134a, dimethylether, R152a, CH₃I (R13I1), propane, isopropane, propylene, isobutane,n-butane, HFO1234yf, and a combination thereof, and the absorbentcomprises components of the working fluid and a solvent selected fromthe group consisting of N-methyl-2-pyrrolidone (NMP), dimethyl sulfoxide(DMSO), dimethylformamide (DMF), dimethylacetamide (DMAc), and acombination thereof; removing heat from the absorber; increasing thepressure of at least a portion of the liquid solution by a pressureboosting device to obtain a higher pressure liquid solution; separatingat least a portion of the higher pressure liquid solution in a generatorto obtain at least a higher pressure, substantially vaporized stream ofthe working fluid and a higher pressure, liquid stream of the absorbent;substantially condensing at least a portion of the higher pressure,substantially vaporized stream of the working fluid in a condenser toobtain a substantially condensed stream of the working fluid; cooling atleast a portion of the substantially condensed stream of the workingfluid in a heat exchanger to obtain a sub-cooled stream of the workingfluid, while heating another stream; reducing the pressure of at least aportion of the sub-cooled stream of the working fluid to obtain a lowerpressure stream of the working fluid; vaporizing at least a portion ofthe lower pressure stream of the working fluid in an evaporator toobtain an at least partially vaporized stream of the working fluid,while removing heat from another heat source, wherein the other heatsource in the vaporizing step is heat from environment of an enclosedspace or a process stream when the thermally activated process is usedfor heating the enclosed space or the process stream, or heat from anenclosed space or a process stream when the thermally activated processis used for cooling the enclosed space or the process stream, and theother stream in the heat exchanger comprises the at least partiallyvaporized stream of the working fluid from the evaporator, heating ofwhich results in the lower pressure, substantially gaseous stream of theworking fluid; feeding at least a portion of the lower pressure,substantially gaseous stream of the working fluid to the absorber;cooling at least a portion of the higher pressure, liquid stream of theabsorbent in a second heat exchanger to obtain a sub-cooled, liquidstream of the absorbent; reducing the pressure of at least a portion ofthe sub-cooled, liquid stream of the absorbent to obtain the lowerpressure, liquid stream of the absorbent; and feeding at least a portionof the lower pressure, liquid stream of the absorbent to the absorber.16. The thermally activated process of claim 15, wherein the second heatexchanger cools at least a portion of the higher pressure, liquid streamof the absorbent from the bottom section of the generator to obtain thesub-cooled, liquid stream of the absorbent, while heating and partiallyvaporizing at least a portion of the higher pressure, liquid solutionfrom the pressure boosting device to obtain a higher pressure, two-phasestream, at least a portion of which is subsequently fed to anintermediate location of the generator.
 17. The thermally activatedprocess of claim 16, wherein the portion of the higher pressure, liquidsolution being heated and partially vaporized constitutes 80-99% (mol)of the higher pressure, liquid solution, and 1-20% (mol) of the higherpressure, liquid solution is sent to the top of the generator withoutbeing heated and partially vaporized.
 18. The process of claim 17,wherein the higher pressure, substantially vaporized stream of theworking fluid obtained from the generator contains up to 5% (mol) of thesolvent, and the at least partially vaporized stream of the workingfluid obtained from the evaporator contains 0.1-5% (mol) liquid.
 19. Thethermally activated process of claim 11, wherein the separating steputilizes more than one generators.
 20. A power generation process,comprising a. the thermally activated process of claim 12, b. expandingat least a portion of the higher pressure, substantially vaporizedstream of the working fluid in an expander to generate mechanicalenergy, and c. absorbing at least a portion of the exhaust stream of theworking fluid from the expander into the lower pressure, liquid streamof the absorbent in the absorber.